The invention refers to a luminaire with at least one LED (light emitting diode) as a light source. Such a light source has a limited light emitting angle for emitted light radiation.
A corresponding emitting angle for such an LED is, for example, between 15° and 120°, wherein such emitting angle generally is determined by a little lens structure of the LED. Concerning such light sources, it has to be considered, that even in the case that the efficiency is relatively high, with such LEDs, for example, a maximum of 20% of the input energy is converted to visible light. The remaining energy input is converted to heat. To avoid any damage to the LED by such produced heat, this heat will generally be dissipated by a cooling body, active cooling, liquid cooling, or the like. Otherwise, the lifetime of such an LED and also its light output will be negatively influenced or reduced by such high heat input. As a rule it might be said that at temperatures of 120° C. or more, a corresponding semi-conductor crystal of the LED is damaged resulting in permanent impairment to functional life, light color, light output or other drawbacks to the LED. In the case of explosion-proof luminaires, it has to be considered that by passing a critical temperature value such an LED will have a particular ignition effectiveness, which can result in danger to body and life. To prevent this, suitable measurements have to be taken to prevent an overrun of such critical temperature (generally temperatures classes or ignition temperature of a gas-air mixture, in which the explosion protection operation means is used).